In a case where a plurality of synchronous motors connected in parallel and mechanically coupled to each other is driven by a single power converter, a phase sequence of a part of the plurality of synchronous motors may be wrongly wired. Here, it is assumed that the phase sequence of a single synchronous motor be wrongly wired. In this case, the synchronous motor which is wrongly wired is driven by being pulled by an output torque of the normally wired synchronous motor. Therefore, a speed of the plurality of synchronous motors can be adjusted according to a command value. On the other hand, an excessive current flows through the synchronous motor which is wrongly wired. When the excessive current flows through the synchronous motor, the motor may burn. Therefore, a technology for accurately detecting the miswired state of the plurality of synchronous motors is required.
It is assumed that at least one phase of at least one winding group be disconnected in a case where a synchronous motor having a winding structure in which a plurality of winding groups having three winding parts connected in a Y-shape is electrically connected in parallel is driven. In this case, since the synchronous motor is driven by being gulled by a phase which is not disconnected, the speed of the synchronous motor can be adjusted according to the command value. On the other hand, an excessive current flows through the phase of the synchronous motor which is not disconnected. When the excessive current flows through the synchronous motor, the synchronous motor may burn. Therefore, a technology for accurately detecting the disconnection of the synchronous motor having the plurality of groups of winding structures is required.
Patent Literature 1 discloses a control apparatus for a three-phase induction motor having a miswiring detection function. In the control apparatus in Patent Literature 1, a method is disclosed in which a value obtained by dividing an increase in an amplitude of a voltage command value by an increase in a primary frequency is calculated and it is determined that at least one induction motor of which the phase sequence is wrongly wired exists when the calculation result falls below a reference value.
Patent Literature 2 discloses an electric vehicle control device having a disconnection detection function. The control device in Patent Literature 2 calculates a torque of an induction motor based on a q-axis current, a d-axis current, a q-axis voltage command, a d-axis voltage command, and an inverter angular frequency and outputs a disconnection detection signal when a difference between the maximum value of the calculated torque and the minimum value exceeds a torque fluctuation range reference value.